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Low-cost solution-based synthesis of metal halide perovskites (MHPs) invariably introduces defects in the system, which could form Shockley-Read-Hall (SRH) electron-hole recombination centers detrimental to solar conversion efficiency. Here, we investigate the nonradiative recombination processes due to native point defects in methylammonium lead halide (MAPbI 3 ) perovskites using ab initio nonadiabatic molecular dynamics within surface-hopping framework. Regardless of whether the defects introduce a shallow or deep band state, we find that charge recombination in MAPbI 3 is not enhanced, contrary to predictions from SRH theory. We demonstrate that this strong tolerance against defects, and hence the breakdown of SRH, arises because the photogenerated carriers are only coupled with low-frequency phonons and electron and hole states overlap weakly. Both factors appreciably decrease the nonadiabatic coupling. We argue that the soft nature of the inorganic lattice with small bulk modulus is key for defect tolerance, and hence, the findings are general to other MHPs.
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Extending Carrier Lifetimes in Lead Halide Perovskites with Alkali Metals by Passivating and Eliminating Halide Interstitial Defects
Abstract Defects, such as halide interstitials, act as charge recombination centers, induce degradation of halide perovskites, and create major obstacles to applications of these materials. Alkali metal dopants greatly improve perovskite performance. Using ab initio nonadiabatic molecular dynamics, it is demonstrated that alkalis bring favorable effects. The formation energy of halide interstitials increases by up to a factor of four in the presence of alkali dopants, and therefore, defect concentration decreases. When defects are present, alkali metals strongly bind to them. Halide interstitials introduce mid‐gap states that rapidly trap charge carriers. Alkalis eliminate the trap states, helping to maintain high current density. Further to charge trapping, the interstitials accelerate charge recombination. By passivating the interstitials, alkalis make carrier lifetimes up to seven times longer than in defect‐free perovskites and up to thirty times longer than in defective perovskites.
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- Award ID(s):
- 1900510
- PAR ID:
- 10132976
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 12
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 4684-4690
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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